Question:
Mendelian Disorders
Read the following passage carefully and answer the given questions.
Genetic disorders may be grouped into two categories - Mendelian disorders and Chromosomal disorders. Mendelian disorders are mainly determined by alteration or mutation in a single gene. These disorders are transmitted to the offspring on the same lines as in the principle of inheritance. The pattern of inheritance of such Mendelian disorders can be traced in a family by pedigree analysis. Most common and prevalent Mendelian disorders are Haemophilia, Cystic fibrosis, Sickle-cell anaemia, Colour blindness, Phenylketonuria, Thalassemia, etc. The Mendelian disorders may be dominant or recessive. By pedigree analysis, one can easily understand whether the trait in question is dominant or recessive. Similarly, the trait may also be linked to the sex chromosome or an autosome.
Which one of the following substitutions is a cause of sickle-cell anaemia?
Mendelian Disorders
Read the following passage carefully and answer the given questions.
Genetic disorders may be grouped into two categories - Mendelian disorders and Chromosomal disorders. Mendelian disorders are mainly determined by alteration or mutation in a single gene. These disorders are transmitted to the offspring on the same lines as in the principle of inheritance. The pattern of inheritance of such Mendelian disorders can be traced in a family by pedigree analysis. Most common and prevalent Mendelian disorders are Haemophilia, Cystic fibrosis, Sickle-cell anaemia, Colour blindness, Phenylketonuria, Thalassemia, etc. The Mendelian disorders may be dominant or recessive. By pedigree analysis, one can easily understand whether the trait in question is dominant or recessive. Similarly, the trait may also be linked to the sex chromosome or an autosome.
Which one of the following substitutions is a cause of sickle-cell anaemia?
Read the following passage carefully and answer the given questions.
Genetic disorders may be grouped into two categories - Mendelian disorders and Chromosomal disorders. Mendelian disorders are mainly determined by alteration or mutation in a single gene. These disorders are transmitted to the offspring on the same lines as in the principle of inheritance. The pattern of inheritance of such Mendelian disorders can be traced in a family by pedigree analysis. Most common and prevalent Mendelian disorders are Haemophilia, Cystic fibrosis, Sickle-cell anaemia, Colour blindness, Phenylketonuria, Thalassemia, etc. The Mendelian disorders may be dominant or recessive. By pedigree analysis, one can easily understand whether the trait in question is dominant or recessive. Similarly, the trait may also be linked to the sex chromosome or an autosome.
Which one of the following substitutions is a cause of sickle-cell anaemia?
Show Hint
Remember Glu to Val at position 6 of the beta chain (GAG to GTG).
Updated On: Oct 1, 2026
- Substitution of valine by aspartic acid at the sixth position of the beta globin chain.
- Substitution of glutamic acid by alanine at the sixth position of the beta globin chain.
- Substitution of glutamic acid by valine at the sixth position of the beta globin chain.
- Substitution of glycine by methionine at the sixth position of the beta globin chain.
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The Correct Option is C
Solution and Explanation
Step 1: Understanding the Concept:
Sickle-cell anaemia is caused by a point mutation in the beta globin gene. The base change GAG to GTG changes one amino acid in the beta chain of haemoglobin.
Step 2: Recall the exact change:
At the sixth position of the beta globin chain, glutamic acid (a charged, acidic amino acid) is replaced by valine (a non-polar amino acid). The changed haemoglobin sticks together under low oxygen and bends the red cell into a sickle shape.
Step 3: Check the options:
Option 3 states exactly this change. Option 1 has the amino acids the wrong way round and uses aspartic acid. Option 2 uses alanine, which is not involved. Option 4 uses glycine and methionine, which are also not involved.
Final Answer:
Glutamic acid is replaced by valine at the sixth position of the beta chain, which is option 3.
Sickle-cell anaemia is caused by a point mutation in the beta globin gene. The base change GAG to GTG changes one amino acid in the beta chain of haemoglobin.
Step 2: Recall the exact change:
At the sixth position of the beta globin chain, glutamic acid (a charged, acidic amino acid) is replaced by valine (a non-polar amino acid). The changed haemoglobin sticks together under low oxygen and bends the red cell into a sickle shape.
Step 3: Check the options:
Option 3 states exactly this change. Option 1 has the amino acids the wrong way round and uses aspartic acid. Option 2 uses alanine, which is not involved. Option 4 uses glycine and methionine, which are also not involved.
Final Answer:
Glutamic acid is replaced by valine at the sixth position of the beta chain, which is option 3.
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